The broad objective of this project is to understand the molecular basis of recombination in Escherichia coli following conjugation. Studies would be directed toward elucidation of the composition of the recombinant molecule. The juxtaposition of old and new F minus DNA and old and new Hfr DNA in recombinational intermediates will be investigated to determine whether there are unique arrangements resulting from the recombination process. ("Old" DNA is defined as DNA made in parents before mating, "new" DNA is DNA made during mating.) The polarity relationships between the old and the new Hfr DNA which is transferred and integrated during conjugation will be determined. The general method used is one of differential labeling with both density and radioactive isotopes of parental bacteria both before and during mating, followed by identification and characterization of recombinant molecules isolated from the mated recipient cells. That class of recombinant DNA's which contain material derived from both parental DNA's in proportions that are not the same as replicated parental DNA's will be isolated by CsCl density gradient equilibrium centrifugation. In order to identify the full range of compostions of recombinant DNA, a biological assay using transformation will be employed to survey all density classes of DNA isolated from mated bacteria. Experiments of a different sort are also planned which would allow an expansion of the horizons of experiments on recombination mechanisms: an effort will be made to develop an in vitro assay for recombination. Such an assay would establish a system which would permit isolation and characterization of cellular components which are active in different steps of the recombination process.